The present invention relates to controlling a heating system. More particularly, the present invention relates to a method and apparatus for causing a heating system controller to change modes of operation.
There are many uses for industrial heating systems such as ovens, furnaces and boilers. Many such heating systems are sold by Original Equipment Manufacturers (OEM's). However, before OEM's can sell such heating systems, they are generally required to check out the operation of the heating system for any flaws. In order to check out the heating system, the OEM's cause the heating system controller to control operation of the heating system such that the heating system is run through a check-out sequence. During the check-out sequence, the heating system controller exercises all critical functions of the heating system so that check-out personnel can verify correct operation of the heating system and controller.
Some heating systems are controlled by a microprocessor. Therefore, in order to cause the heating system controller to perform the check-out sequence, a signal must be provided to the microprocessor so the microprocessor can enter a check-out mode.
In the past, there were several techniques for causing the microprocessor to enter the check-out mode. In one technique, the microprocessors used in heating system controllers had a designated pin for receiving the check-out mode signal. Upon receiving a check-out mode signal, the microprocessor would change from a normal operation mode to a check-out mode during which it cycled through the check-out sequence. In a second technique, heating system controllers had extra hardware added to facilitate the change between the normal mode of operation and the check-out mode. By manipulating inputs to this extra hardware, the OEM operator could command the microprocessor to enter the check-out mode.
However, as heating system controllers have become more complex, and as more control parameters are sensed by the heating system controller in controlling the heating system, the availability of pins on the microprocessor used in the heating system controller has declined. Also, the amount and complexity of the extra hardware required to accomplish the change between a normal operation mode and a check-out mode has increased. This has caused heating system controller hardware to grow to an undesirable size, or in some cases, has caused heating system controller manufacturers to increase the number of pins available on the microprocessor unit used in the heating system controller. For example, some heating system controllers now require a 40 pin microprocessor rather than a 28 pin processor. Both the increase in hardware and the increase in processor size are costly in terms of space and component cost.
For these reasons, there is a continuing need for the development of improved techniques for causing heating system controllers to change between a normal operation mode and a check-out mode. Further, there is a continuing need for developing these techniques which use no extra microprocessor pins and no extra hardware.